Conventional motor vehicles are generally designed with an engine cooling system including a liquid coolant that circulates about the engine block to transfer heat away from the engine during operation. The cooling system also generally includes a radiator to disperse the heat absorbed by the liquid coolant. Many motor vehicles are also designed with an air conditioning system that includes an air conditioning coolant condenser, such as Freon, which also operates to disperse heat.
To facilitate the dispersion of heat from vehicle engine cooling and air conditioning systems, motor vehicles generally include a fan to drive air over the radiator and condenser at lower vehicle speeds where air flow over the radiator and condenser is minimal. The fan can be engaged by a fan clutch independently responsive to either engine coolant temperature or air conditioning coolant gas pressure within the condenser.
In operation, however, this design can suffer from various problems. For example, the fan is generally engaged only as long as the engine temperature or condenser pressure exceed given set points. Thereafter, the fan is disengaged and the engine temperature or condenser pressure again begin to increase to the point where the fan is once again engaged. During low speed operation of the vehicle, and especially during idle conditions, this can result in excessive cycling of the fan mechanism as well as frequent temperature and condenser pressure switch failure. Excessive cycling problems are generally compounded during operation of the air conditioning system when either the engine temperature or condenser pressure can independently cause the cooling fan to be engaged.
Switch failure, as well as temperature or pressure detector failure, can result in rapid engine or air conditioning system overheating. Excessive cycling of the fan mechanism reduces fan mechanism lifespan and overall engine fuel economy and may result in increased difficulty in system troubleshooting. Inadequate cooling can secondarily result in poor reliability of system components. Finally, conventional engine fans lack controlled responsiveness to the cooling requirements of other vehicle system including transmission fluid, power steering fluid and especially air-to-air intercoolers.
Various systems have been implemented in an effort to address some of these problems. One such system is disclosed in U.S. Pat. No. 4,425,766 issued to Claypole. Claypole discloses a motor vehicle cooling fan power management system comprising a microprocessor based electronic control unit for engine fan control in response to engine temperature, engine speed, vehicle road speed and the on/off state of the air conditioning system. Depending on the cooling needs of the engine, the duration of a constant voltage signal to the engine cooling fan is varied via a pulse-width modulator. The voltage signal is directly operative to drive the engine cooling fan at variable speeds.
However, Claypole fails to overcome over-heating problems associated with failure of temperature or pressure switches and detectors. Claypole also fails to address control of the cooling requirements of other vehicle systems including transmission fluid, power steering fluid and air-to-air intercoolers. Moreover, the use of microprocessors increases the expense of the system and, absent additional logic circuits, limits the number of inputs for the purposes of controlling fan operation based on other vehicle operating systems. The use of microprocessors also increases the electromagnetic radiation of the system thereby creating greater interference with other electronic vehicle systems.
Additionally, the Claypole system discloses an engine fan driven directly by a voltage signal from a pulse width modulator. As a result, the Claypole system is operable only with smaller motor vehicles, such as passenger cars, which do not utilize engine cooling fans having high horsepower requirements. Larger motor vehicles having engine cooling fans with high horsepower requirements, such as heavy duty trucks, would suffer significantly reduced engine efficiency upon operation of the engine cooling fan under the Claypole system. Finally, such a pulse width modulation system is neither compatible with, nor directed to the efficient control of an engine fan clutch.
U.S. Pat. No. 4,546,742 issued to Sturges discloses a temperature control system for an internal combustion engine having a variable speed cooling fan. The Sturges system utilizes a pulse width modulation voltage signal generator to alternatively open and close a solenoid valve thereby controlling a fluid pressure level operative to drive the cooling fan. As a result, however, the Sturges system is neither compatible with, nor directed to the efficient control of an engine fan clutch.
U.K. Patent Application No. 2,142,445 A discloses a cooling-fan driving control system for a vehicle utilizing an electronic control unit for controlling engine fan clutch and fan operation responsive to engine coolant temperature, engine speed and engine load. The system utilizes digital logic to engage the engine fan when coolant temperature exceeds a high selected temperature, and to disengage the engine fan when coolant temperature is below a low selected temperature. When coolant temperature is between the high and low selected temperatures, the engine fan is controlled solely in response to engine speed and load.
U.S. Pat. No. 4,804,139 issued to Bier discloses a cooling system for water-cooled vehicle engines that utilizes dual engine coolant temperature detectors and an override responsive to temperature detector failure to control engine fan operation. However, Bier is a microprocessor based system. As such, it includes the attendant problems associated therewith such as added expense, limited input, and increased electromagnetic radiation.
U.S. Pat. No. 4,930,320 issued to Ide et al discloses a cooling fan controlling apparatus for vehicle with air conditioner. Ide et al utilizes a digital electronic control unit responsive to the vehicle air conditioning system to control engine fan operation. U.S. Pat. No. 4,651,922 issued to Noba and Japanese Patent No. 58-39513 disclose engine fan control systems utilizing dual cooling fans for greater cooling capacity. U.S. Pat. No. 4,848,100 issued to Barthel et al discloses a system for controlling refrigerant flow in an air conditioning system.
The prior art devices discussed above provide a general background in respect of the control of engine cooling fans. These devices suffer variously from lack of universal response to multiple vehicle systems requiring cooling, lack of compatibility with a variety of motor vehicle cooling systems, and complex components.